Probe tack

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

In another tack test, a steel ball of specified diameter is rolled down a grooved incline onto a conditioned surface area of pressure sensitive adhesive (ASTM D 3121, PSTC-6). The length of travel before it stops is the rolling ball tack (Fig. 2d) reported in millimeters. It is relatively inexpensive and simple to set up. Similar test variables to the probe tack test apply. 

Fig. 2. Tack tests and results, (a) Probe tack, (b) Probe tack vs. temperature for a natural rubber PSA. (c) Loop tack, (d) Rolling ball.

Probe tack. A probe (flat or not) is contacted with an adhesive film at a given pressure and dwell time. The force required to remove the probe from the adhesive is a measure of tack [30]. 

Fig. 18 a Schematic of probe tack measurements of a thin adhesive film along a temperature gradient, b Compilation of probe tack data during loading and unloading cycles for different temperatures. c Total adhesion energy, calculated from the area under the load-displacement curve shown in b divided by maximum contact area, as a function of temperature. The error bars represent one standard deviation of the data, which is taken as the experimental uncertainty of the measurement. (Reproduced with permission from [86])... 

Moon SH, Chiche A, Forster AM, Zhang WH, Stafford CM (2005) Evaluation of temperature-dependent adhesive performance via combinatorial probe tack measurements. Rev Sci lustrum 76 062210... 

The holding power, adhesion, and probe tack of selected pressure-sensitive adhesive sheets were evaluated in accordance with JIS Z0237. Testing results are provided in Table 2. 

EHA), vinyl acetate (VAc) and acrylic acid (AA), and with varying contents of 2-hydroxyefhyl methacrylate (2-HEMA) and an unsaturated benzophenone derivative (P-36). The UV-crosslinking behavior of the PSAs was monitored by FTIR-ATR and PSA performance was evaluated by probe tack, peel strength, and shear adhesion failure temperature (SAFT) after exposure to various UV doses. 

Fig. 17.5 shows the change of probe tack with varying 2-HEMA contents at various UVdoses. The probe tack of SH3P1, SH6P1, and SH9P1 decreased dramatically at a UV dose of 210 mj cm , but at above 630 mj cm the probe tack decreased only slightly. The relative decrease (D) in probe tack at 210 mJ cm compared with probe tack before UV exposure was calculated by means of Eq. (1). 

Fig. 17.5 Change of probe tack in SHOPl, SH3P1, SH5P1, and SH9P1 with variation in UV dose.

Probe tack and peel strength test methods are almost same, except for test area and test time, in that the measurements are taken with the PSA removed from the substrate. So the peel strength is influenced by the Tg also, so that if the Tg of a PSA is sufficiently low, the wettability will increase after applying it... 

Fig. 13 (a) Comparison of the probe-tack stress-strain curves for the model PBA adhesive in the presence of 2.7 wt% clay-armored soft-hard hybrid particles with the equivalent amount of non-armored PLA (2.45 wt%), Laponite clay discs (0.25 wt%), and a blend of non-armored PLA (2.45 wt%) and Laponite clay (0.25 wt%). (b) Synergistic effect of PLA-nanoclay hybrid particles on the tack energy of the model PSA. 

Figure 4. Sample B Real Time Probe Tack Debonding Force vs. Displacment.

By automating the standard PSA testing methods for probe tack and shear adhesion, it was clearly demonstrated that one obtains statistically more significant data very efficiently. 

For probe tack, the newly measured debonding energies constitute a new dimension for short duration performance. In addition to the peak force, tack energy should be considered in many high speed applications. Since the peak force and tack energy appeared to have originated from different parts of the viscoelastic spectra, it offered an opportunity to adjust the formulation for optimum performance. 

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